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Abstract:

To provide an image forming apparatus including: a discharge tray which
can moves between a first position capable of loading a discharged sheet
and a second position that is separated from the first position; and a
sheet loading amount detection sensor which has a sheet detection flag
abutting against the upper surface of the sheet loaded on the discharge
tray and capable of moving in accordance with a loading amount of the
sheet loaded on the discharge tray, and detects the sheet loading amount
by detecting a position of the sheet detection flag, wherein when the
discharge tray means is located at the second position, the sheet
detection flag is removed from a position capable of detecting the sheet
loading amount.

Claims:

1-12. (canceled)

13. An image forming apparatus capable of attaching a discharge tray which
loads a discharged sheet from a main body of the apparatus, or a sheet
post-processing device which performs processing to the discharged sheet
alternatively to the main body, comprising:a sheet loading amount
detection sensor which has a sheet detection flag abutting against the
upper surface of the sheet loaded on the discharge tray, and detects the
sheet loading amount,wherein when the sheet post-processing device is
attached to the main body, the sheet detection flag is located at a
retracting position retracted from a detecting position capable of
detecting the sheet loading amount of the sheet loaded on the discharge
tray.

14. An image forming apparatus according to claim 13, wherein the sheet
detection flag is moved to the retracting position when the discharge
tray is detached from the main body.

15. An image forming apparatus according to claim 14, further
comprising:an attachment detection sensor which detects that the
discharge tray is attached to the main body,wherein when the attachment
detection sensor detects that the discharge tray is not attached to the
main body, a detection signal from the sheet loading amount detection
sensor is ignored.

16. An image forming apparatus according to claim 13, wherein the sheet
detection flag is located at a standby position intersecting a sheet
carry-in path of the sheet post-processing device when the sheet
post-processing device is connected to the main body.

17. An image forming apparatus according to claim 16, wherein the sheet
detection flag is pressed against the sheet and it can move to a sheet
entrance detection position when the sheet enters the sheet
post-processing device from the main body.

18. An image forming apparatus according to claim 17, wherein a sheet
entrance detection sensor that is disposed at the sheet post-processing
device detects that the sheet detection flag moves to the sheet entrance
detection position.

19. An image forming apparatus according to claim 17, wherein a sheet
entrance detection sensor that is disposed at the main body detects that
the sheet detection flag moves to the sheet entrance detection position.

21. An image forming apparatus according to claim 13, further comprising:a
first attachment detection sensor which detects that the discharge tray
is attached to the main body; anda second attachment detection sensor
which detects that the sheet post-processing device is attached to the
main body.

22. An image forming apparatus according to claim 21, wherein it is
recognized that the sheet post-processing device is normally connected to
the main body when the first attachment detection sensor detects that the
discharge tray is not attached to the main body, the second attachment
detection sensor detects that the sheet post-processing device is
attached to the main body, and detecting the electric connection between
the main body and the sheet post-processing device.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to an image forming apparatus such as
a printer for printing the digital information by using an electro
photography, a multifunctional printer mounting an image reading
apparatus at its upper part on the printer body as a base, and a printer
provided with a sheet processing device or the like.

[0003]2. Description of the Related Art

[0004]Depending on digitalization of the information and an IT revolution
or the like, a printer as one example of an image forming apparatus has
been widely used and developed from a business use to a personal use and
from monochrome to color. On the other hand, development of
digitalization contributes to a complex function of the printer.
Therefore, a printer characterized as an output of an information
terminal such as a personal computer or the like so far has been
characterized also as a product to integrate the functions such as a
copying machine, a facsimile machine, and an image input apparatus or the
like that are independent functions conventionally.

[0005]It is because a technical base of developing a new product
characterized by a high cost performance and a little space such as
plural functions by one machine has been put into place. A typical
example of the product is a MFC (multifunction copier) which is made by
digitalizing and giving a network function to the conventional copying
machine or a MFP (multifunction printer) which is made by giving an image
input function to the conventional printer.

[0006]According to such an image forming apparatus, a printed sheet is
reversed in the middle of a path to convey the sheet by a sheet reversing
apparatus that is provided in the image forming apparatus so as to be
so-called FD (face down) discharged from a sheet discharge port disposed
on a side of the image forming main body of the apparatus to a loading
tray. Alternatively, without reversed, the printed sheet passes through
the path so as to be so-called FU (face up) discharged from the sheet
discharge port to the loading tray (refer to JP-A-09-086757).

[0007]According to such a conventional image forming apparatus, in the
case that a sheet post-processing device for performing the processing to
the sheet is not mounted, the sheet to be discharged from the discharge
port of the image forming main body of the apparatus is discharged on the
loading tray that is disposed at the side of the body. If a predetermined
amount of the sheet is loaded on the loading tray, when the load amount
attains to a predetermined upper limit a full load detection sensor flag
that is disposed on the side of the image forming apparatus is mounted on
the uppermost sheet, the full load detection sensor flag turns off a full
load detection sensor, and the image forming apparatus stops its
operation by an OFF signal from the full load detection sensor.

[0008]On the other hand, a sheet post-processing device may be disposed at
the side surface of the sheet discharge port side. As the sheet
post-processing device, a staple stacker has been known, which is
disposed at the side surface of the sheet discharge port side of the
image forming main body of the apparatus, adjusts respective end portions
of the sheets sequentially fed from the sheet discharge port of the image
forming main body of the apparatus, carries out the post-processing such
as staple (pin) or the like, and discharge the sheets.

[0009]However, according to such a conventional image forming apparatus,
when carrying out the operation such as jam clearance operation or the
like at the periphery of the sheet discharge port, it is necessary to
detach the parts such as an exterior at the periphery of the sheet
discharge port and the sheet post-processing device. In this case, the
full load detection sensor flag is left at an initial position.
Therefore, the full load detection sensor flag interferes with the
operation such as the jam clearance operation or the like and this
sometimes involves a problem that the full load detection sensor flag is
damaged.

[0010]In addition, the configuration of a connection part becomes
complicated upon installation of the image forming apparatus on the sheet
post-processing device, so that there is a problem that the cost becomes
high and reliability is lowered due to increase of the number of the
parts.

SUMMARY OF THE INVENTION

[0011]The present invention has been made taking the foregoing problems
into consideration and an object of which is to provide an image forming
apparatus with a high usability and a high reliability.

[0012]In order to attain the above-described object, the present invention
may provide an image forming apparatus comprising: a discharge tray which
can moves between a first position capable of loading a discharged sheet
and a second position that is separated from the first position; and a
sheet loading amount detection sensor which has a sheet detection flag
abutting against the upper surface of the sheet loaded on the discharge
tray and capable of moving in accordance with a loading amount of the
sheet loaded on the discharge tray, and detects the sheet loading amount
by detecting a position of the sheet detection flag; wherein, when the
discharge tray is located at the second position, the sheet detection
flag is removed from a position capable of detecting the sheet loading
amount.

[0013]According to the present invention, by moving the discharge tray to
be separated from the position where the sheets are loaded when carrying
out the operation such as the jam clearance operation or the like at the
periphery of the sheet discharge port, a sheet detection flag is removed
from a position where it can detect the amount of the sheet loading (move
to an removal position). Therefore, the sheet detection flag can evade
damage of the sheet detection flag without interfering with the operation
such as the jam clearance operation or the like and it is possible to
provide an apparatus with a high usability and a high reliability.

[0014]In addition, since the sheet detection flag is removed to the
removal position upon installation of the sheet post-processing device on
the image forming apparatus, there is no fear that the sheet loading
amount detection sensor is damaged by interference with the connection
part at the side of the sheet post-processing device. Further, since the
sheet detection flag functions as an in-sensor flag for detecting
entering of the sheet into the sheet post-processing device, the
configuration of the connection part between the image forming apparatus
and the sheet post-processing device can be simplified, and since the
number of the parts is decreased, it is possible to lower the cost.
Further, since the configuration is simplified, it is possible to provide
an apparatus with a high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a longitudinal sectional view showing a schematic
configuration of an image forming apparatus according to a first
embodiment;

[0016]FIG. 2 is a longitudinal sectional view showing a state that a
discharging tray is installed in the image forming apparatus according to
the first embodiment;

[0017]FIG. 3 is a longitudinal sectional view showing schematic
configurations of the image forming apparatus and a sheet post-processing
device according to the first embodiment;

[0018]FIG. 4 is a longitudinal sectional view showing a state that the
sheet post-processing device according to the first embodiment is not
installed;

[0019]FIG. 5 is a table showing a connection state of the image forming
apparatus and the sheet post-processing device according to the first
embodiment;

[0020]FIG. 6 is a flow chart showing the operation state of the image
forming apparatus according to the first embodiment;

[0021]FIGS. 7A and 7B is an enlarged longitudinal sectional view showing
the operation of the full load detection sensor flag when a sheet
proceeds into the sheet post-processing device from the image forming
apparatus according to a second and third embodiment;

[0022]FIGS. 8A to 8D is a sectional view showing a positional relation
between the full load detection sensor flag and a sheet in-sensor
according to the second embodiment;

[0023]FIG. 9 is a cross sectional view showing schematic configurations of
the image forming apparatus and a sheet post-processing device according
to the second embodiment;

[0024]FIGS. 10A to 10D is a sectional view showing a positional relation
between the full load detection sensor flag and a sheet in-sensor
according to the third embodiment;

[0025]FIG. 11 is a cross sectional view showing schematic configurations
of an image forming apparatus and a sheet post-processing device
according to the third embodiment;

[0026]FIG. 12 is a longitudinal sectional view showing a schematic
configuration of an image forming apparatus according to a fourth
embodiment; and

[0027]FIG. 13 is a longitudinal sectional view showing a state that a
discharging tray of the image forming apparatus according to the fourth
embodiment is folded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]The preferred embodiments of the present invention will be described
in detail with reference to the drawings below. However, a scope of the
present invention is not limited only to a measurement, a material, a
shape, and a relative position of a constituent part described in this
embodiment unless there is a special description.

[0029]In the following respective embodiments, an example of an image
forming apparatus represented by a multifunction printer of a laser
printer base will be described.

A First Embodiment

(Description of an Image Forming Apparatus)

[0030]With reference to FIGS. 1 to 6, the image forming apparatus
according to the first embodiment will be described below.

[0032]On the basis of the image data read by the image reading unit or the
like, the writing scanner 14 may write a latent image on the image
forming drum 10. The written latent image is developed by a toner of the
image forming process unit 9. The sheet which is taken out from the sheet
feeding cassette 2 by the sheet feeding roller 3 is separated into one by
one via the pair of separation and transport rollers 4, and passes
through the transport paths 6 and 7. Then, the sheet is fed to the image
forming drum 10 with synchronized at the resist roller 8 and a toner
image on the image forming drum 10 is transferred on the sheet. The sheet
on which the toner image is transferred is fed to a fixing device 11 to
be pressurized with heat by the pair of fixing discharge rollers 12 and
the toner image is fused and fixed on the sheet.

[0033]In this case, a discharge tray 40 as an example of the loading means
is disposed on the side surface of the image forming main body of the
apparatus. In order to discharge the sheet on this discharge tray 40, two
discharge paths are set. At first, an A transport path 15 is provided,
whereby the sheet is U-turned and fed on the upper part of the writing
scanner 14 by the pair of fixing discharge rollers 12 to be reversed and
discharged; and a B transport path 30 for directly discharging the sheet
on the discharge tray 40.

[0034]Switching to the A transport path 15 is carried out by an FD/FU
flapper 21 to be disposed at a downstream side of the pair of fixing
discharge rollers 12. A junction roller pair 16 is disposed at a
downstream side of the flapper 21 and at the middle part of the A
transport path 15 and a reverse roller pair 17 is disposed at the upper
part of the image forming unit. This reverse roller pair 17 is configures
so as to reverse the direction of transportation of the sheet in order to
feed the sheet to a C transport path 33 described below.

[0035]A lead-in transport path 18 is formed at a further downstream side
of the reverse roller pair 17 and the lead-in transport path 18 is
configured in such a manner that its end portion passes over the image
forming process unit 9 and comes round the image forming process unit 9
so as to prevent a sheet end from getting out of the apparatus. At the
middle part of the A transport path 15, a sheet detection sensor 19 is
also disposed.

[0036]Switching to the B transport path 30 to directly discharge the sheet
to the discharge tray 40 is carried out by the FD/FU flapper 21 and the
sheet is discharged to the discharge tray 40 via a discharge roller pair
32. In the case of discharging the sheet via this B transport path 30,
the sheet is discharged to the discharge tray 40 with faced up.

[0037]The C transport path 33 is provided to connect the reverse roller
pair 17 to the discharge roller pair 32, and at the upstream of the
discharge roller pair 32, a sheet detection sensor 34 is provided.

[0038]In addition, before the reverse roller pair 17 and in the vicinity
of the junction portion of the A transport path 15 and the C transport
path 33, a reverse flapper 35 is provided. This reverse flapper 35 is
always biased to a side to block the A transport path 15 and the reverse
flapper 35 may be pushed and released by a transportation force of the
sheet, for example, by setting a light bias force. Alternatively, the
transport path may be switched at timing by a solenoid or the like.

[0039]In the case of discharging the sheet via the A transport path 15 and
the C transport path 33, the sheet is discharged to the discharge tray 40
with faced down.

[0040]At a full load detection sensor flag 50 as an example of the sheet
detection part, a full load detection sensor light shielding part 53 is
disposed at a swing center 51. When discharging and loading the sheet
from the image forming apparatus 1 to the discharge tray 40, before the
sheet is loaded to a predetermined height, the full load detection sensor
light shielding part 53 disposed at the full load detection sensor flag
50 shields the light from a full load detection sensor 52.

[0041]When the sheet is discharged or the sheet is loaded to a
predetermined height, a front end of the full load detection sensor flag
50 is loaded on the upper surface of the sheet to be swing around the
swing center 51. In addition, also by the discharge operation of the
sheet, the full load detection sensor flag 50 swings and the full load
detection sensor light shielding part 53 does not shield the light from
the full load detection sensor 52, so that the full load detection sensor
52 may detect timing of next shielding and detect that the sheet is
normally discharged. In addition, detecting that the light from the full
load detection sensor 52 has not been shielded continuously over a
predetermined time (normally, time sufficiently longer than time of
discharging one sheet), the full load detection sensor 52 may detect that
the loading height of the sheet on a tray 42 as a loading part attains to
the upper limit and the image forming apparatus 1 may stop.

[0042]In the meantime, according to the present embodiment, detecting that
the full load detection sensor light shielding part 53 has not shield the
light from the full load detection sensor 52 during a predetermined time,
the full load state is determined, however, detecting that the full load
detection sensor light shielding part 53 has shield the light from the
full load detection sensor 52 during a predetermined time, the full load
state may be determined.

(Explanation of Slide Operation of a Discharge Tray)

[0043]In order to describe the operation of the full load detection sensor
flag 50 with reference to FIGS. 1 and 2, a case that the sheet is left in
the B transport path 30 and a case that the sheet post-processing device
is attached to the image forming apparatus 1 will be described below.

[0044]The discharge tray 40 shown in FIG. 1 is composed of a load wall 41,
a tray 42, a rail 43 fixed at front and rear sides of the tray 42, an
exterior cover (not illustrated), and a flip-up member 45 or the like.

[0045]The rail 43 is disposed as a bar-type rail on the discharge tray 40
and gains entrance into the image forming apparatus 1.

[0046]By rollers 81 and 82 that are disposed at a frame of the image
forming apparatus 1 to freely swing with respect to axes 85, 86 that are
disposed at the frame, the rail 43 may support a weight of the discharge
tray 40 slidably in a horizontally direction.

[0047]An FU guide 60 composing a guide at the outside of the B transport
path 30 may rotate around a swing center 61 by its own weight in a
counterclockwise direction. The position of the FU guide 60 is limited as
shown in FIG. 2 by abutting the flip-up member 45 disposed at the
discharge tray 40 against the FU guide 60.

[0048]A projection 47 is disposed at the discharge tray 40. A discharge
tray detection member 46 is provided to freely swing around a swing
center and it is biased by a spring in a counterclockwise direction. As
shown in FIG. 2, when the tray 42 is located at a first position in which
the tray 42 can receive and carry the discharged sheet upon the normal
operation of the image forming apparatus 1, the projection 47 presses the
discharge tray detection member 46; then, the discharge tray detection
member 46 swings in a clockwise direction to press a discharge tray
switch 49 as one example of the position detection means; and the
discharge tray switch 49 is turned on. As a result, the image forming
apparatus 1 may detect that the tray 42 is located at the first position.

[0049]FIG. 1 shows a state that the discharge tray 40 is pulled out. In
the case that a user carries out the jam clearance operation for the
sheet that is left in the B transport path 30, the user pulls out the
tray 42 to a left side, namely, to a second position with putting his or
her hand on a handle to make the state shown in FIG. 1.

[0050]When the flip-up member 45 is removed to a left side in conjunction
with the slide operation of the discharge tray 40 and the FU guide 60
swings about the swing center 61, the B transport path 30 is sufficiently
released so as to enable accessing to the sheet in the B transport path
30.

[0051]Thus, when the tray 42 is located at the second position to which
the tray 42 is pulled out, the projection 47 is separated from the
discharge tray detection member 46, so that the discharge tray detection
member 46 biased by the spring while swings in a counterclockwise
direction and separated from the discharge tray switch 49. Accordingly,
since the discharge tray switch 49 is turned off, the image forming
apparatus 1 detects that the tray 42 is pulled out to be located at the
second position.

[0052]If the user completes the jam clearance operation of the sheet, the
user may slide the discharge tray 40 to the right side. By abutting
against the FU guide 60, the flip-up member 45 swings in a clockwise
direction, and when the tray 42 slides to the first position, the B
transport path 30 which is in a state of transporting the sheet is
formed.

[0053]Due to these configurations, in conjunction with the slide operation
of the discharge tray 40, the B transport path 30 is opened and closed,
and this makes it possible for the user to easily carry out the jam
clearance operation of the sheet.

(Explanation with Regard to the Removal Operation of the Full Load
Detection Sensor Flag)

[0054]As shown in FIG. 2, when the tray 42 is located at the first
position, the projection 47 may press the discharge tray detection member
46 to swing it to a predetermined position. In this time, the full load
detection sensor flag 50 may swing by its own weight about the swing
center 51 to be located at a predetermined standby position. The full
load detection sensor 52 uses a photo sensor.

[0055]Then, if the sheet is continuously loaded on the tray 42, the full
load detection sensor flag 50 contacts the upper surface of the sheet,
and further, if the sheet is continuously loaded to a predetermined upper
limit, the full load detection sensor light shielding part 53 of the full
load detection sensor flag 50 does not shield the light from the full
load detection sensor 52, so that it is detected that the sheet on the
tray 42 attains to the limit amount of loading.

[0056]When the tray 42 slides from the image forming apparatus 1 to the
left side to be located at the second position (FIG. 1), the projection
47 is separated from the discharge tray detection member 46 and the
discharge tray detection member 46 is biased by the spring to swing to a
predetermined position. In this case, the discharge tray detection member
46 flips up a branch portion that is branched and elongated from the
swing center 51 of the full load detection sensor flag 50, and the full
load detection sensor flag 50 swings to a predetermined removal position
in a direction represented by an arrow in FIG. 1. The removal position of
the full load detection sensor flag 50 is a position where the user's
hand does not contact the full load detection sensor flag 50 when the
user inserts his or her hand inside of the image forming apparatus 1 to
carry out the jam clearance operation.

[0057]If the user completes the jam clearance operation of the sheet, the
user may slide the discharge tray 40 to the right side. When the tray 42
is located at the first position, the projection 47 may press the
discharge tray detection member 46 to swing it to a predetermined
position. Then, the discharge tray detection member 46 is separated from
the branch portion of the full load detection sensor flag 50 and the full
load detection sensor flag 50 may return to a predetermined standby
position by its own weight.

[0058]As described above, since the removal position of the full load
detection sensor flag 50 is a position where the user does not contact
the full load detection sensor flag 50 upon the jam clearance operation,
the user can carry out the jam clearance operation without interfered by
the full load detection sensor flag 50 and this makes it possible to
improve the operationality. In addition, since there is no possibility to
accidentally damage the full load detection sensor flag 50, the
reliability can be improved.

(Explanation with Regard to Attachment of a Sheet Post-processing Device)

[0059]A case that the discharge tray 40 that is attached in a default
configuration is removed from the image forming apparatus 1 and the sheet
post-processing device is attached will be described below.

[0060]In FIG. 3, a staple stacker 200 capable of adjusting a plurality of
sheets and carrying out the processing to put the sheets in a folder is
attached as an example of sheet post-processing device.

[0061]At first, sliding the discharge tray 40 to a position that can be
slid at the maximum, the discharge tray 40 is pulled out from the image
forming apparatus 1.

[0062]The staple stacker 200 is provided with a rail 243 equivalent to the
rail 43 that is disposed on the discharge tray 40. In addition, a flip-up
member 247 equivalent to the flip-up member 45 is also disposed (refer to
FIG. 4), and the configuration of the interface with respect to the image
forming apparatus 1 is the same as the discharge tray 40.

[0063]As shown in FIG. 4, since the interface to be connected to the image
forming apparatus 1 is completely the same as the discharge tray 40 in
the staple stacker 200, if the discharge tray 40 is slid to the right
side in a direction opposite to the process to take out the discharge
tray 40, the staple stacker 200 can be attached to the image forming
apparatus 1.

[0064]The image forming apparatus 1 is provided with a projection 62. In
the staple stacker 200, a sheet post-processing device switch 249 and a
sheet post-processing device switch member 246 as an example of the
attachment detection means are provided. If the staple stacker 200 is not
attached to the image forming apparatus 1, the sheet post-processing
device switch member 246 is biased by the spring in a clockwise
direction.

[0066]The staple stacker 200 is provided with one end of a cable (not
illustrated) and when the staple stacker 200 is attached to the image
forming apparatus 1, the other end of the cable is connected to the image
forming apparatus 1. Communication of an electric signal is carried out
between the staple stacker 200 and the image forming apparatus 1 via the
cable.

[0067]In the meantime, in order to detect with or without of the sheet
post-processing device, means for detecting that the cable is connected
may be provided or by detecting that the image forming apparatus 1 is
communicated with the staple stacker 200, with or without of the sheet
post-processing device may be detected.

[0068]As shown in FIG. 4, even in the case that the stable stacker 200 is
pulled out to the left side for the jam clearance processing, one end of
the cable has a length enough to prevent separation from the connection
to the image forming apparatus 1.

[0069]As shown in the table in FIG. 5, there are six patterns of
connection conditions of the image forming apparatus 1, the discharge
tray 40, and the staple stacker 200. When fully detecting that the
discharge tray switch 49 is turned off, the sheet post-processing device
switch 249 is turned on, and the staple stacker 200 is electrically
connected to the image forming apparatus 1 via the cable, it is
recognized that the staple stacker 200 is normally connected to the image
forming apparatus 1.

[0070]Then, when detecting that a full load detection sensor disposed to
the staple stacker 200 (not illustrated) is turned off as shown in FIG.
6, the image forming apparatus 1 and the staple stacker 200 may normally
operate.

[0071]In the next place, the case that the sheet enters in the sheet
post-processing device from the image forming apparatus 1 will be
described below.

[0072]The staple stacker 200 is provided with a sheet carry-in path 202 to
receive the sheet discharged from the image forming apparatus 1 and guide
the sheet to the next processing and operation.

[0073]As shown in FIG. 4, in the vicinity of the sheet carry-in path 202,
a sheet in-sensor 203 and an in-sensor flag 205 are disposed as one
example of sheet entrance detection means. According to the present
embodiment, as the sheet in-sensor 203, a photo sensor is employed.

[0074]The sheet transported from the image forming apparatus 1 is carried
in the sheet carry-in path 202 within the staple stacker 200 to abut
against the in-sensor flag 205. Then, swinging the in-sensor flag 205
about the swing center to shield the light from the sheet in-sensor 203,
it is detected that the sheet enters inside of the staple stacker 200.

[0075]After that, the staple stacker 200 may carry out a sequence of the
post-processing operation on the basis of a signal from the sheet
in-sensor 203.

[0076]As described above, when the tray 42 moves from the first position
to the second position upon loading of the sheet, at the same time, the
full load detection sensor flag 50 moves to the removal position. As a
result, when carrying out the operation such as the jam clearance or the
like in the vicinity of the sheet discharge port, the full load detection
sensor flag 50 does not interfere with such operation and the full load
detection sensor flag 50 can be prevented from damaged, so that it is
possible to provide an apparatus with a high usability and a high
reliability.

[0077]In addition, the configuration that the full load detection sensor
flag 50 moves only when the tray 42 moves from the first position to the
second position is described according to the present embodiment,
however, it is also possible to obtain the same advantage with respect to
the configuration that the full load detection sensor flag 50 moves by
attachment and detachment of the sheet post-processing device.

[0078]In addition, according to the present embodiment, the configuration
that the full load detection sensor flag 50 moves to the removal position
by means of the force applying means is described, however, it is also
possible to obtain the same advantage with respect to the configuration
that the full load detection sensor flag 50 moves to the removal position
by using an electronic part such as a motor or the like.

A Second Embodiment

[0079]In the next place, the case that the sheet enters in the sheet
post-processing device from the image forming apparatus will be described
below. In the meantime, the elements described according to the above
embodiment are given the same reference numerals and explanation thereof
is not repeated here. According to the present embodiment, without
providing a flag for an in-sensor to the sheet post-processing device,
the full load detection sensor flag 50 of the image forming apparatus 1
functions as the flag for the in-sensor of the sheet post-processing
device.

[0080]The staple stacker 200 is provided with the sheet carry-in path 202
to receive the sheet discharged from the image forming apparatus 1 and
guide the sheet to the next processing and operation.

[0081]FIG. 9 is a cross sectional view seeing the connection part of the
image forming apparatus 1 and the staple stacker 200 from an upper
direction. In the vicinity of the sheet carry-in path 202, the sheet
in-sensor 203 is disposed as one example of sheet entrance detection
means. According to the present embodiment, as the sheet in-sensor 203, a
photo sensor is employed. The full load detection sensor flag 50 is
provided with the full load detection sensor light shielding part 53 and
an in-sensor light shielding part 54 at the swing center 51 as shown in
FIGS. 8A to 8D. The in-sensor light shielding part 54 may shield the
light form the sheet in-sensor 203.

[0082]FIG. 7A shows a state that a sheet S does not enter the sheet
carry-in path 202. In this case, the full load detection sensor flag 50
is located at a predetermined standby position. In this standby position,
the front end of the full load detection sensor flag 50 intersects the
sheet carry-in path 202 and the full load detection sensor flag 50 is
arranged substantially in parallel with a direction of transportation of
the sheet so as not to interfere with transportation of the sheet. This
standby position is obtained in such a manner that the full load
detection sensor flag 50 swings about the swing center 51 by its own
weight till it abuts against the discharge tray detection member 46 when
the not illustrated projection that is disposed at the exterior part of
the staple stacker 200 abuts against the discharge tray detection member
46 and the discharge tray detection member 46 swings to a predetermined
position. Since the full load detection sensor light shielding part 53 of
the full load detection sensor flag 50 does not shield the light from the
full load detection sensor 52 in this time, this state is same as the
full loading state. However, since the discharge tray switch 49 is not
turned on, the image forming apparatus 1 may ignore a detection signal
from the full load detection sensor 52.

[0083]FIG. 7B shows a state that a sheet S enters the sheet carry-in path
202. In this time, the full load detection sensor flag 50 is pressed by
the sheet S and the full load detection sensor flag 50 may swing about
the swing center 51 to the position where its front end is mounted on the
upper surface of the sheet S.

[0084]FIGS. 8A to 8D show a positional relation between the full load
detection sensor flag 50 and a sheet in-sensor 203. At the swing center
51 of the full load detection sensor flag 50, the full load detection
sensor light shielding part 53 and the in-sensor light shielding part 54
are provided. FIG. 8A shows the state that the sheet is not full loaded
on the discharge tray 40; FIG. 8B shows the state that the sheet is full
loaded on the discharge tray 40; and FIG. 8C shows a position of the full
load detection sensor flag 50 when the discharge tray 40 is not attached.
Attaching the staple stacker 200, in accordance with swinging of the load
detection sensor flag 50, the in-sensor light shielding part 54 shields
the light from the sheet in-sensor 203 as shown in FIG. 8D, it is
detected that the sheet enters inside of the staple stacker 200.

[0085]After that, the staple stacker 200 may carry out a sequence of the
post-processing operation on the basis of a signal from the sheet
in-sensor 203.

[0086]As described above, without providing a flag for an in-sensor to the
sheet post-processing device, the full load detection sensor flag 50 of
the image forming apparatus 1 functions as the flag for the in-sensor of
the sheet post-processing device, so that since the number of parts is
decreased, the cost can be lowered, and since the configuration of the
apparatus is simplified, it is possible to provide an apparatus with a
high reliability.

[0087]According to the present embodiment, the configuration that the
sheet post-processing device can be attached when the discharge tray 40
of the image forming apparatus 1 is taken off is described as above,
however, according to the image forming apparatus 1 and the sheet
post-processing device that are configured so as to attach the sheet
post-processing device at the discharge port of the image forming
apparatus 1 without taking off the discharge tray 40, the same advantage
can be obtained.

A Third Embodiment

[0088]In the next place, the case that the sheet post-processing device is
attached to the image forming apparatus 1 and the full load detection
sensor at the side of the image forming apparatus 1 functions as the
in-sensor for carrying the sheet from the image forming apparatus 1 to
the sheet post-processing device will be described below. In the
meantime, the matters described according to the above-described
embodiments are given the same reference numerals and the explanation
thereof is not repeated here.

[0089]FIG. 11 is a cross sectional view seeing the connection part of the
stable stacker 200 and the image forming apparatus 1 from an upper
direction. In the vicinity of the swing center 51 of the full load
detection sensor flag 50, the full load detection sensor 52 as an example
of the sheet detection means is provided. According to the present
embodiment, as the full load detection sensor 52, a photo sensor is
employed. As shown in FIG. 10, the full load detection sensor flag 50 is
provided with the full load detection sensor light shielding part 53 and
the in-sensor light shielding part 54 at the swing center 51. The full
load detection sensor light shielding part 53 and the in-sensor light
shielding part 54 may shield the light from the full load detection
sensor 52.

[0090]When the sheet S does not enter the stable stacker 200 as shown in
FIG. 7A, the full load detection sensor flag 50 described according to
the first embodiment is located at a predetermined removal position. This
predetermined removal position is a position where the front end of the
full load detection sensor flag 50 intersects the sheet carry-in path
202.

[0091]FIGS. 10A to 10D show a positional relation between the full load
detection sensor flag 50 and the full load detection sensor 52. FIG. 10A
shows the state that the sheet is not full loaded on the discharge tray
40 and FIG. 10B shows a position of the full load detection sensor flag
50 upon the full loading. When the discharge tray 40 is not attached, the
full load detection sensor light shielding part 53 may swing only to a
position where the full load detection sensor light shielding part 53
does not shield the light from the full load detection sensor 52 as shown
in FIG. 10C. The control of the full load detection sensor 52 may switch
from a sensor for detecting the number of the sheets on the discharge
tray 40 of the image forming apparatus 1 into a sensor for detecting the
sheet to be carried in the staple stacker 200 (FIG. 10D) when it is
detected that the staple stacker 200 is normally connected to the image
forming apparatus 1.

[0092]As shown in FIG. 7B, the full load detection sensor flag 50 is
pressed by the sheet S which is transported to the staple stacker 200 and
the full load detection sensor flag 50 may swing about the swing center
51 to the position where its front end is mounted on the upper surface of
the sheet S. Accordingly, as shown in FIG. 10D, the in-sensor light
shielding part 54 passes through the full load detection sensor 52; the
full load detection sensor 52 detects that the sheet enters the staple
stacker 200; and transmits an electric signal to the staple stacker 200
via the cable (not illustrated). After that, the staple stacker 200 may
carry out a sequence of the post-processing operation on the basis of a
signal from the image forming apparatus 1.

[0093]As described above, without providing an sheet in-sensor to the
sheet post-processing device, the full load detection sensor 52 of the
image forming apparatus 1 functions as the sheet in-sensor of the sheet
post-processing device, so that since the configuration of the connection
part of the image forming apparatus 1 and the sheet post-processing
device is simplified and the number of parts is decreased, the cost can
be lowered, and the configuration is simplified, thus it is possible to
provide an apparatus with a high reliability.

[0094]According to the present embodiment, the configuration that the
sheet post-processing device can be attached after the full load
detection sensor flag 50 moves to the predetermined removal position when
the discharge tray 40 of the image forming apparatus 1 moves from the
first predetermined position to the second predetermined position when
the sheet is loaded is described, however, also according to the
configuration that the full load detection sensor flag 50 moves to the
predetermined removal position by attaching the sheet post-processing
device to the image forming apparatus 1 that is configured so that it is
possible to attach the sheet post-processing device to the discharge port
of the image forming apparatus 1 without moving the discharge tray 40 to
the second predetermined position, the same advantage can be obtained.

A Fourth Embodiment

[0095]In addition, also according to the configuration that the loading
part moves from the first position to the second position with folded,
the same advantage can be obtained. In the meantime, the matters
described according to the above-descried embodiments are given the same
reference numerals and its explanation is not repeated here.

[0096]The configuration that a sub tray 74, a base tray 75, and the load
wall 41 constructing the loading part of the discharge tray 40 are folded
to move from the first position to the second position will be described
below. As shown in FIG. 12, the sub tray 74 may swing centering on a
swing center 72 in a clockwise direction to move on the base tray 74. In
the next place, the base tray 75 may swing about the swing center 73 in a
clockwise direction to move to a predetermined position in front of the
load wall 41.

[0097]Further, the sub tray 74, the base tray 75, and the load wall 41
that are folded as shown in FIG. 13 may swing from the first position to
the second position about a swing center 71 in a clockwise direction to
move to the second position. In this case, the projection 47 is separated
from the discharge tray detection member 46 and the discharge tray
detection member 46 is biased by the spring to swing to a predetermined
position. In this case, the discharge tray detection member 46 flips up
the full load detection sensor flag 50, and the full load detection
sensor flag 50 may swing to a predetermined removal position. The removal
position of the full load detection sensor flag 50 is a position where
the user's hand does not contact the full load detection sensor flag 50
when the user inserts his or her hand inside of the image forming
apparatus 1.